Cleaning device for cleaning process gas of a reflow soldering system

ABSTRACT

The present invention is directed to a cleaning device for process gases of a reflow soldering system that includes a plurality of cleaning chambers. The plurality of cleaning chambers contain a cleaning liquid for the process gas, where each of the cleaning chambers is adapted to be flown through via a supply line for the contaminated process gas and via a discharge line for the cleaned gas. The cleaning chambers also include a plurality of cleaning walls along which the cleaning liquid is flown for take-up of impurities in the process gas into the cleaning liquid. A plurality of the deposition walls is provided, where at least one of the deposition walls also forms an outer wall of the cleaning device.

BACKGROUND

The present invention relates to a cleaning device for process gasesparticularly of a reflow soldering system, the device comprising aplurality of cleaning chambers containing a cleaning liquid for theprocess gas, each of the cleaning chambers being adapted to be flownthrough via a supply line for the contaminated process gas and adischarge line for the cleaned process gas.

Cleaning devices for reflow soldering gases are e.g. known from the USpatent provided with U.S. Pat. No. 4,951,401. Said cleaning devicescomprise a channel with the help of which the process gas is taken fromthe reflow soldering system and supplied again to the system afterhaving been cleaned by means of a filter. Impurities deriving from theprocess gas are retained by the filter, which can be replaced or washedas soon as its absorbing capacity has been exhausted. A further cleaningdevice for process gases of a reflow soldering system is described in JP59-029020 A. In this system, the process gas is passed through acleaning liquid.

A cleaning device for exhaust gases issuing from combustion processes isdescribed in DE 37 27 2943 A1. Said device comprises a tubular housingwhich can be divided by so-called gas distributor plates into severaldeposition chambers for the process gas. The number of the employed gasdistribution plates depends on the length of the tubular housing.

SUMMARY

It is the object of the present invention to provide a cleaning devicefor the process gas particularly of a reflow soldering system with thehelp of which a comparatively efficient cleaning of the process gas canbe effected independently of the general conditions set by the system.

According to the invention this object is achieved in that the cleaningchambers are each formed by modules of which such a great number isarranged to be flown through in parallel that the required throughput ofprocess gas is achieved, and of which such a great number is arranged tobe flown through one after the other that the required degree of purityis achieved for the process gas. The impurities issuing from the processgas can be discharged to the cleaning liquid by contacting the processgas with the cleaning liquid. In this process, the cleaning device canadvantageously be adapted to the required deposition performance in anoptimum way in that the modules are connected in parallel in response tothe required throughput of process gas and in series in response to therequired residual content of impurities. It is particularly possible toconnect modules of different operative principles in series to be ableto achieve the required degree of deposition and to filter, forinstance, impurities with different properties in an optimum way. Theindividual modules employed can be configured to have a simpleconstruction and a small constructional size, so that e.g. with the helpof plug-type connections it is easily possible to create cleaningdevices offering the possibility of a finely graded capacity adaptation.

A further advantage is that the enhancement of the depositionperformance is not limited by a rise in the loss of pressure produced bythe cleaning device.

An additional advantage in the use of cleaning liquid is due to the factthat said liquid can be exchanged without the process sequence of thereflow soldering system being stopped. The removed and contaminatedcleaning liquid can here be replaced by a clean cleaning liquid at thesame time. Since standstill times of the reflow soldering system areavoided, profitability during operation of a reflow soldering systemprovided with the cleaning device according to the invention canadvantageously be enhanced.

It is advantageous when modules with different operative principles arearranged one after the other in series during deposition. In this case,it is e.g. possible to employ, first of all, an operative principle witha high absorption capacity with respect to impurities, whereby theprocess gas can first be freed within a short period of time from themajority of impurities. Subsequently, an operative principle may e.g. beemployed with a high performance with respect to the attainable residualconcentration, so that a high degree of purity of the cleaned processgas can be set.

According to a variant of the invention a flow path for the cleaningliquid extends through the series-connected modules such that thedirection of flow of the cleaning liquid is opposite to the direction offlow of the process gas. This advantageously improves the depositionperformance of the cleaning device of the invention through realizationof a counter-current principle.

According to a further variant of the module-like construction, cleaningliquids with different cleaning properties may be provided in thecleaning chambers of the parallel-connected modules. It is therebypossible to select different cleaning liquids, each being advantageouslyadapted in an optimum way to different substances to be separated.Optimum cleaning results can respectively be achieved with said cleaningliquids. When different cleaning liquids are used, it is particularlyadvantageous to series-connect the modules with respect to the processgas to be cleaned because the process gas will then pass in one cyclethrough all of the different cleaning liquids.

According to a further variant of the invention, the cleaning chambercontains a bath consisting of the cleaning liquid, the supply lineterminating below the liquid level of the bath in said bath. It isthereby possible in an advantageous way to pass the process gas in theform of bubbles through the bath, whereby the surface is enlarged thatis available for discharging the impurities from the process gas to thecleaning liquid. At the same time the construction of said cleaningmeans is very simple, whereby an inexpensive production is made possiblein an advantageous way.

According to another variant of the invention the cleaning chambercomprises at least one deposition wall on the surface of which a film ofthe cleaning liquid is provided. An exactly defined deposition surfacecan thereby be formed in an advantageous way, the deposition surfacebeing defined by the surface of the cleaning-liquid film formed on thedeposition wall.

It is advantageous when the deposition wall is arranged perpendicular orwith a slope in the cleaning chamber and when in the area of a topdeposition-wall edge which is obtained due to said arrangement, a supplymeans for the cleaning liquid is arranged that is directed thereto. Thishas the effect that the cleaning liquid flows, starting from the topedge of the deposition wall in the manner of a waterfall and inconformity with gravity, downwards along said wall, and the cleaningliquid can thus be replaced without any problems.

According to another variant of the invention, at least one injectionopening for the cleaning liquid is directed into the cleaning chamber.The cleaning liquid can be distributed by means of preferably aplurality of injection openings in the cleaning chamber, whereby amixture is formed with the process gas to be cleaned. Advantageously,the surface which is available for absorbing impurities in the cleaningfluid is thereby enlarged. For instance, a liquid curtain can be formedthrough which the process gas is passed. The injection openings,however, may also be configured in the form of nozzles, so that a liquidmist can be produced in the cleaning chamber.

A further variant of the invention is characterized by a combination ofseveral modules, each containing a cleaning chamber, in such a mannerthat a process gas can flow through all of the cleaning chambers. It ishere possible to achieve the combination, on the one hand, as a parallelconnection of a plurality of modules, whereby the capacity of thecleaning device can advantageously be adapted to different reflowsoldering systems. The constructional efforts are here small and thereduction of individual components has an advantageous effect on storagein the marketing of the cleaning device. Another possibility is providedby the series-connection of modules, whereby the cleaning device can bemodified with respect to the quality of the deposition result.Particularly modules with different operative principles, e.g. themodules already described above, can be connected one after the other,so that the advantages of the individual operative principles can becombined with one another.

Advantageously, the cleaning chamber may comprise an outlet which isconnected to a clarifying device for the cleaning liquid. The clarifyingdevice may e.g. consist of a clarifying tank in which the impuritiesintroduced into the cleaning liquid can settle as sludge. This sludgecan then be disposed off easily while the clarified cleaning liquid canbe returned again to the cleaning process. This offers the possibilityof using the cleaning liquid repeatedly, whereby profitability duringoperation of the cleaning device can be further enhanced in anadvantageous manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention shall now be described in the followingwith reference to the drawing, in which

FIG. 1 shows one possibility of connecting a cleaning device to a reflowsoldering system, in a schematic section;

FIGS. 2 to 4 shows possible operative principles for cleaning deviceswith a cleaning liquid, in a schematic section; and

FIG. 5 is a schematic and partly cut-open illustration of an embodimentof the cleaning device according to the invention in a modulararrangement.

DETAILED DESCRIPTION

FIG. 1 shows a cleaning device 11 which is connected via a supply line12 and a discharge line 13 to a reflow soldering system 14 in such amanner that the process gas contained in the reflow soldering system issupplied to the cleaning device in the manner as outlined by arrows andcan be returned into the reflow soldering system 14 after the cleaningprocess has been carried out, resulting in a circulatory flow for theprocess gas. The cleaning device includes a cleaning chamber 15 which ispartly filled with a cleaning liquid 16. At an interface 17 between thecleaning liquid 16 and the process gas contained in the cleaning chamber15, impurities are exchanged from the process gas into the cleaningliquid.

With a clarifying device 18 in the form of a clarifying tank, thecleaning liquid 16 forms a circulatory flow which is completed via asupply 19 to the cleaning device and via an outlet 20 away from thecleaning device. In the clarifying device 18, the impurities transferredfrom the process gas into the cleaning liquid 16 settle down as sludge21. The sludge can be removed via an outlet valve 22 from the clarifyingdevice.

Inert liquids such as water or oils may e.g. be used as cleaningliquids, said liquids being non-reactive with constituents of theprocess gas. Of particular advantage is the use of so-calledperfluoropolyethers, which are soluble neither in water nor in oil andare characterized by a high resistance to reactive chemicals.

Further embodiments of cleaning means shall be explained in thefollowing; components which are configured in accordance with theembodiment shown in FIG. 1 are provided with the same reference numeralsand shall not be explained in more detail.

The cleaning device 11 according to FIG. 2 is of a cylindricalconfiguration and is predominantly filled with the cleaning liquid 16.The cleaning liquid is continuously exchanged via inlet 19 and outlet20.

The process gas is supplied via the supply line 12 and a distributor 23below the liquid level of the cleaning liquid 16, so that the processgas can be cleaned while rising upwards in small bubbles 23 in thecleaning liquid.

Deposition walls 25, which are partly formed by the outer wall of thecleaning device 11 at the same time, are provided in the cleaningchamber 15 of the cleaning device 11 according to FIG. 3. Supply means27 which are connected to the supply for the cleaning liquid (not shownin more detail in FIG. 3) are provided on the upper edges 26 of thedeposition walls. As outlined, the supply means 27 wet the depositionwalls 25 with the cleaning liquid, so that said liquid flows down alongthe walls and is collected in the lower portion of the cleaning deviceat outlet 20. A film 28 of the cleaning liquid is formed in this processon the deposition walls 25, with the process gas sweeping along saidfilm.

The cleaning device 11 shown in FIG. 4 is provided in the cleaningchamber 15 with a plurality of injection openings 29 which are connectedto supply 19. The injection openings in their entirety produce a rain-or mist-like curtain 30 in the cleaning chamber 15, the process gasbeing passed through said curtain. The cleaning liquid is collected inthe lower part of the cleaning chamber in the area of outlet 20.

FIG. 5 shows a modular construction of the cleaning device 11 by way ofexample. Modules 31 a, 31 b are represented in a simplified manner asboxes, two of said boxes being cut open. As can be seen from theillustrated cut-open modules, two modules with different operativeprinciples are series-connected each time. Modules 31 a have apre-cleaning function and employ the operative principle shown in FIG.2. Modules 31 b have a final cleaning function, the operative principleof FIG. 4 being here employed. Of course, any other desired combinationof operative principles is possible.

The cleaning liquid is first supplied to modules 31 b and then tomodules 31 a. Therefore, a cleaning liquid slightly subjected toimpurities is first available for the final cleaning process, wherebythe efficiency of the final cleaning process is improved. The cleaningliquid is subsequently used for the pre-cleaning process where acleaning effect is possible due to the still high concentration ofimpurities in the process gas. As for the flow directions of cleaningliquid and process gas, the counter-current principle is thus realizedaccording to FIG. 5. However, a co-current principle is just as wellpossible if this seems to be more appropriate for the specific case ofapplication. Moreover, it is also possible to use different cleaningliquids in modules 31 b and 31 a for subjecting the process gas insuccessive order to different cleaning steps (not shown).

While the series-connection of the modules 31 a and 31 b improves thecleaning action of the cleaning device 11, the parallel arrangement ofthe respective module combination 31 a, 31 b aims at an enhancement ofthe possible throughput of process gas. As a consequence, the modularcleaning device 11 can be adapted to reflow soldering systems havingdifferent capacities.

1. A cleaning device for process gases that is configured to generateclean process gas from contaminated process gas in a reflow solderingsystem, comprising: a cleaning chamber comprising first and secondseries-connected modules, configured to have different operativeprinciples of deposition, which are connected one after the other inseries, wherein the first series-connected module comprises, a cleaningliquid configured to clean the contaminated process gas, said cleaningchamber allowing the contaminated process gas to flow therein via asecond series-connected module and allowing the cleaned process gas toflow therefrom via a discharge line; a first deposition wall having afirst surface, the surface being configured to receive a film of thecleaning liquid and being configured to be an outer wall of the cleaningdevice; and a second deposition wall positioned centrally within thecleaning chamber and having a second surface facing the first surface,the second surface being configured to receive another film of thecleaning liquid; and wherein the second series-connected modulecomprises, a bath comprising the cleaning liquid, and a supply linecoupled below a liquid level of the bath and configured to allow thecontaminated process gas to flow therein and rise upwards in bubbles inthe bath.
 2. The device according to claim 1, wherein a flow path forthe cleaning liquid extends through the series-connected modules in sucha manner that the direction of flow of the cleaning liquid is oppositeto the direction of flow of the process gas.
 3. The cleaning deviceaccording to claim 1, wherein there are a plurality of the first andsecond deposition walls that are arranged perpendicular or with a slopewith respect to each other in the cleaning chamber and a supply for thecleaning liquid is arranged in an area on top of edges of the pluralityof first and second deposition walls.
 4. The cleaning device accordingto claim 1, wherein at least one respective injection opening for thecleaning liquid is directed into the cleaning chamber.
 5. The cleaningdevice according to claim 1, wherein the cleaning chamber comprises arespective outlet that is connected to a clarifying device for thecleaning liquid.
 6. The cleaning device according to claim 1, whereinthe cleaning device comprises a plurality of cleaning chambers arrangedin parallel configured to allow for a predetermined throughput and, insuccessive order, to allow for a predetermined degree of purity for theprocess gas.
 7. The cleaning device according to claim 6, furthercomprising a plurality of cleaning liquids having different cleaningproperties, such that respective ones of which are provided inrespective ones of the plurality of cleaning chambers arranged in thesuccessive order.
 8. A system, comprising: a cleaning chamber comprisingfirst and second series-connected modules, configured to have differentoperative principles of deposition, which are connected one after theother in series, wherein the first series-connected module comprises, aplurality of separate deposition walls each having a surface, thesurface being configured to receive a film of a cleaning liquid that isconfigured to clean a contaminated process gas, the contaminated processgas flowing into the plurality of separate deposition walls via a secondseries-connected module and from the plurality of separate depositionwalls via a discharge line, wherein a supply for the cleaning liquid isarranged in an area on top of edges of the plurality of separatedeposition walls, wherein at least one of the plurality of separatedeposition walls is an inner surface of an outer wall of the system, andwherein a respective one of the plurality of separate deposition wallsis centrally located within the system and has first and secondsurfaces, the first and second surfaces each being configured to receiveanother film of the cleaning liquid; and wherein the secondseries-connected module comprises, a bath comprising the cleaningliquid, and a supply line coupled below a liquid level of the bath andconfigured to allow the contaminated process gas to flow therein andrise upwards in bubbles in the bath.
 9. The device according to claim 8,wherein a flow path for the cleaning liquid extends through theseries-connected modules in such a manner that the direction of flow ofthe cleaning liquid is opposite to the direction of flow of the processgas.
 10. The cleaning device according to claim 8, wherein the pluralityof separate deposition walls are arranged perpendicular or with a slopewith respect to each other.
 11. The cleaning device according to claim8, wherein at least one respective injection opening for the cleaningliquid is directed into the plurality of separate deposition walls. 12.The cleaning device according to claim 8, wherein the plurality ofseparate deposition walls comprises a respective outlet that isconnected to a clarifying device for the cleaning liquid.
 13. The systemaccording to claim 8, wherein the system comprises a plurality ofcleaning chambers arranged in parallel configured to allow for apredetermined throughput and, in successive order, to allow for apredetermined degree of purity for the process gas.
 14. The cleaningdevice according to claim 13, further comprising a plurality of cleaningliquids having different cleaning properties, such that respective onesof which are provided in respective ones of each of the cleaningchambers arranged in the successive order.
 15. A cleaning device forprocess gases that is configured to generate clean process gas fromcontaminated process gas in a reflow soldering system, comprising: acleaning chamber configured to allow the contaminated process gas toflow therein via a supply line and the cleaned process gas to flowtherefrom via a discharge line, the cleaning chamber comprising firstand second series-connected modules, configured to have differentoperative principles of deposition, which are connected one after theother in series, wherein the first series-connected module comprises, atleast one first deposition wall having a first surface, the surfacebeing configured to receive a film of cleaning liquid and beingconfigured to be an outer wall of the cleaning device; at least onesecond deposition wall positioned centrally within the cleaning chamberand having a second surface facing the first surface, the second surfacebeing configured to receive another film of the cleaning liquid; asupply for the cleaning liquid arranged internally in the cleaningchamber in an upper area of the at least one first deposition wall andthe at least one second deposition wall, configured to provide the filmsof cleaning liquid such that the films of cleaning liquid trapcontaminants and flow downward along the at least one first depositionwall and the at least one second deposition wall, the supply for thecleaning liquid constantly replacing the films of cleaning liquid; andan outlet configured to collect the cleaning liquid and trappedcontaminants at a lower area of the cleaning chamber; and wherein thesecond series-connected module comprises a bath comprising the cleaningliquid, and wherein the supply line is coupled below a liquid level ofthe bath and is configured to allow the contaminated process gas to flowtherein and rise upwards in bubbles in the bath.